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234 lines
10 KiB
XML
234 lines
10 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd-fstab-generator">
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<refentryinfo>
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<title>systemd-fstab-generator</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-fstab-generator</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-fstab-generator</refname>
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<refpurpose>Unit generator for /etc/fstab</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-fstab-generator</filename> is a generator
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that translates <filename>/etc/fstab</filename> (see
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<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details) into native systemd units early at boot and when
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configuration of the system manager is reloaded. This will
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instantiate mount and swap units as necessary.</para>
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<para>The <varname>passno</varname> field is treated like a simple
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boolean, and the ordering information is discarded. However, if
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the root file system is checked, it is checked before all the
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other file systems.</para>
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<para>See
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<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for more information about special <filename>/etc/fstab</filename>
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mount options this generator understands.</para>
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<para>One special topic is handling of symbolic links. Historical init
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implementations supported symlinks in <filename>/etc/fstab</filename>.
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Because mount units will refuse mounts where the target is a symbolic link,
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this generator will resolve any symlinks as far as possible when processing
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<filename>/etc/fstab</filename> in order to enhance backwards compatibility.
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If a symlink target does not exist at the time that this generator runs, it
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is assumed that the symlink target is the final target of the mount.</para>
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<para><filename>systemd-fstab-generator</filename> implements
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Kernel Command Line</title>
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<para><filename>systemd-fstab-generator</filename> understands the
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following kernel command line parameters:</para>
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<variablelist class='kernel-commandline-options'>
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<varlistentry>
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<term><varname>fstab=</varname></term>
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<term><varname>rd.fstab=</varname></term>
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<listitem><para>Takes a boolean argument. Defaults to
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<literal>yes</literal>. If <literal>no</literal>, causes the
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generator to ignore any mounts or swap devices configured in
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<filename>/etc/fstab</filename>. <varname>rd.fstab=</varname>
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is honored only by the initial RAM disk (initrd) while
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<varname>fstab=</varname> is honored by both the main system
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and the initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>root=</varname></term>
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<listitem><para>Takes the root filesystem to mount in the
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initrd. <varname>root=</varname> is honored by the
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initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>rootfstype=</varname></term>
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<listitem><para>Takes the root filesystem type that will be
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passed to the mount command. <varname>rootfstype=</varname> is
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honored by the initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>rootflags=</varname></term>
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<listitem><para>Takes the root filesystem mount options to
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use. <varname>rootflags=</varname> is honored by the
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initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>mount.usr=</varname></term>
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<listitem><para>Takes the <filename>/usr</filename> filesystem
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to be mounted by the initrd. If
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<varname>mount.usrfstype=</varname> or
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<varname>mount.usrflags=</varname> is set, then
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<varname>mount.usr=</varname> will default to the value set in
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<varname>root=</varname>.</para>
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<para>Otherwise, this parameter defaults to the
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<filename>/usr</filename> entry found in
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<filename>/etc/fstab</filename> on the root filesystem.</para>
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<para><varname>mount.usr=</varname> is honored by the initrd.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>mount.usrfstype=</varname></term>
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<listitem><para>Takes the <filename>/usr</filename> filesystem
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type that will be passed to the mount command. If
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<varname>mount.usr=</varname> or
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<varname>mount.usrflags=</varname> is set, then
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<varname>mount.usrfstype=</varname> will default to the value
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set in <varname>rootfstype=</varname>.</para>
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<para>Otherwise, this value will be read from the
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<filename>/usr</filename> entry in
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<filename>/etc/fstab</filename> on the root filesystem.</para>
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<para><varname>mount.usrfstype=</varname> is honored by the
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initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>mount.usrflags=</varname></term>
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<listitem><para>Takes the <filename>/usr</filename> filesystem
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mount options to use. If <varname>mount.usr=</varname> or
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<varname>mount.usrfstype=</varname> is set, then
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<varname>mount.usrflags=</varname> will default to the value
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set in <varname>rootflags=</varname>.</para>
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<para>Otherwise, this value will be read from the
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<filename>/usr</filename> entry in
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<filename>/etc/fstab</filename> on the root filesystem.</para>
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<para><varname>mount.usrflags=</varname> is honored by the
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initrd.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.volatile=</varname></term>
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<listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
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special value <option>state</option>.</para>
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<para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
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normal mode.</para>
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<para>If true the generator ensures
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<citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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is run as part of the initial RAM disk ("initrd"). This service changes the mount table before transitioning to
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the host system, so that a volatile memory file system (<literal>tmpfs</literal>) is used as root directory,
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with only <filename>/usr</filename> mounted into it from the configured root file system, in read-only
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mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
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lost at shutdown, as <filename>/etc</filename> and <filename>/var</filename> will be served from the (initially
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unpopulated) volatile memory file system.</para>
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<para>If set to <option>state</option> the generator will leave the root
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directory mount point unaltered, however will mount a <literal>tmpfs</literal> file system to
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<filename>/var</filename>. In this mode the normal system configuration (i.e. the contents of
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<literal>/etc</literal>) is in effect (and may be modified during system runtime), however the system state
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(i.e. the contents of <literal>/var</literal>) is reset at boot and lost at shutdown.</para>
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<para>Note that in none of these modes the root directory, <filename>/etc</filename>, <filename>/var</filename>
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or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
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that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para>
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<para>Note that enabling this setting will only work correctly on operating systems that can boot up with only
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<filename>/usr</filename> mounted, and are able to automatically populate <filename>/etc</filename>, and also
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<filename>/var</filename> in case of <literal>systemd.volatile=yes</literal>.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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